Exhaust gas aftertreatment devices by means of which it is possible to comply with the limits prescribed by future exhaust standards for the pollutant emissions of motor vehicles having an internal combustion engine have a larger overall volume than previous systems and, accordingly, use more space in the vehicle.
At the same time, there are increasingly strict regulations in respect of crash safety and pedestrian protection, to satisfy which new structures or empty spaces in the vehicle are necessary, and these likewise take up space. Structures which may improve crash safety are, for example, auxiliary frames or subframes, in particular “X members”. Empty spaces for pedestrian protection are, in particular, minimum clearances between an engine hood and any other inflexible internal equipment fitted in the engine compartment.
In the case of modern internal combustion engines, the aim is to arrange an exhaust gas aftertreatment device having a catalyst and a particulate filter in the engine compartment, e.g. underneath an exhaust turbocharger. However, it may be too close there to various components for crash safety or brake boosting and, on the other hand, the space above the exhaust gas aftertreatment device cannot be used for any other internal equipment owing to the waste heat of said device.
Other attempts to address vehicle space management include convoluting exhaust flow pathways through an aftertreatment device to increase a distance traveled without increasing an amount of space used by the aftertreatment device. One example approach is shown by Stieglbauer et al. in U.S. Pat. No. 7,900,443. Therein, a particulate filter having a central tubular part and two parts in the form of jackets surrounding the latter and one another, through which, in one embodiment, there is a backward and forward flow in a Z pattern to ensure that the particulate filter heats up rapidly during operation.
A second example approach is shown by Bolander et al. in U.S. Pat. No. 7,210,287. Therein, a vehicle catalyst of similar construction having Z-shaped flow paths from an inlet end to an opposite outlet end, allowing accelerated light off of the catalyst reaction.
A third example approach is shown by Kondo et al. in U.S. Pat. No. 6,065,957. Therein, a catalytic burner for heating or drying, having a pot-shaped housing, in which a hollow-cylindrical catalyst body is situated and at one axial end of which both an inlet opening for combustion air and an exhaust gas outlet opening are arranged. Here, the gas flow through the housing is in a U shape since the gas flows through the cavity in the catalyst body, is then deflected through 180° and then flows through the actual hollow-cylindrical catalyst body.
However, the inventors herein have recognized potential issues with such systems. As one example, exhaust temperatures are desired to be lower due to new emissions standards, which may not rapidly heat the catalyst during cold-starts. Additionally, packaging of the catalysts described above does not sufficiently decrease packaging restraints of the catalyst. As such, a catalytic mass of the catalytic device may be compromised.
It is the underlying object of the present disclosure to specify an exhaust gas aftertreatment device and an arrangement thereof in a motor vehicle, the catalyst of which can be heated up particularly quickly and uniformly during operation and with which the space available in the engine compartment can be increasingly utilized.
In one example, the issues described above may be addressed by an exhaust gas aftertreatment device of a motor vehicle, comprising a catalyst, which is accommodated in a tubular housing which, along its length, has a first end section, a catalyst section, and a connecting section, wherein exhaust gas flows to the connecting section in a direction perpendicular to a central axis of the aftertreatment device, where the exhaust gas flow is divided to flow a first portion centrally to the catalyst and a second portion around the catalyst, wherein the portions are deflected 180° and combined in the first end section, and where the combined portions flow through the catalyst from the first end section to the connecting section. In this way, exhaust gas may warm-up the catalyst before flowing therein.
As one example, the exhaust gas aftertreatment device is designed in such a way that the exhaust gas to be treated enters the exhaust gas aftertreatment device in a region of a connecting section and then a part thereof flows centrally through the catalyst and another part thereof flows around the catalyst at the circumference thereof, wherein the two part flows flowing in the same direction are deflected through 180° and more or less recombined in the first end section and then flow through the catalyst from the end section to the connecting section.
In the present disclosure, the catalyst body is heated both from the inside and from the outside by exhaust gases, wherein both part flows have the same maximum temperature. As a result, the catalyst body can heat up particularly quickly and uniformly during operation, thereby making it possible to satisfy the light off conditions of the exhaust gas aftertreatment device more easily, even with the lower exhaust gas temperatures that are nowadays desired.
Moreover, the U-shaped deflection of the exhaust gases in the catalyst enables the catalyst to be arranged in an engine compartment, namely above an exhaust gas outlet opening of the internal combustion engine, in particular the exhaust gas outlet opening of an exhaust turbocharger. As a result, a region in the engine compartment may be used for the catalyst and/or more volume can be made available for catalytically active material.
Moreover, the catalyst and the housing accommodating the latter can have a relatively short overall length owing to the heating from the inside and from the outside, wherein the tubular housing is pot-shaped, e.g., it resembles a fairly short pipe section closed at one end, the cross section of which will generally be circular but can also be elliptical or polygonal, for example. The small overall length makes it easier to accommodate the catalyst above the exhaust gas outlet opening.
Moreover, there is more space available underneath the exhaust gas outlet opening for additional exhaust gas aftertreatment, e.g. in a particulate filter.
In a corresponding embodiment of the present disclosure, the housing is divided along its length into the end section, the catalyst section, in which the catalyst is accommodated, the connecting section, a particulate filter section, in which a particulate filter arranged downstream of the catalyst is accommodated, and a second end section having a gas outlet opening, wherein the exhaust gas flowing through the catalyst to the connecting section flows in the direction of the particulate filter and then flows through the particulate filter in the direction of the second end section.
In contradistinction to exhaust gas aftertreatment devices known in the art, having a catalyst and a particulate filter in an elongate housing, at one end of which the exhaust gas enters, flows more or less in a straight line through the catalyst and then the particulate filter and then emerges at the other end of the housing, the gas inlet opening in the present disclosure can be situated spatially between the catalyst and the particulate filter, thus allowing the catalyst to be arranged above and the particulate filter below an exhaust gas outlet opening of the internal combustion engine, in particular above and below an exhaust gas outlet opening of an exhaust turbocharger arranged on an exhaust manifold of the internal combustion engine. In this way, the space above the exhaust gas outlet opening is used for the catalyst, and all that extends below this is the particulate filter section of the exhaust gas aftertreatment device, and therefore space is also gained below the exhaust gas outlet opening.
The U-shaped deflection of the exhaust gases in the catalyst and the close coupling of the catalyst and particulate filter in a common housing furthermore have the advantage that the catalyst and the particulate filter both heat up more quickly and more intensively during operation than in separate housings, thereby making it possible to satisfy light-off conditions thereof more easily, even with lower exhaust gas temperatures.
In an embodiment of the present disclosure, the catalyst has a central tubular part, a jacket radially surrounding the central tubular part and through which a part of the exhaust gas flowing in from the gas inlet opening flows centrally, and an outer flow part, which radially surrounds the part in the form of a jacket and through which the other part of the exhaust gas flowing in from the gas inlet opening flows at the circumference of the catalyst, wherein these three parts each extend in the longitudinal direction of the exhaust gas aftertreatment device and are in flow connection with one another in the first end section.
In this case, the exhaust gas aftertreatment device can have a gas inlet opening which is arranged in the region of the connecting section and is in flow connection with the ends, remote from the first end section, both of the central tubular part and of the outer flow part of the catalyst.
The flow connection between the gas inlet opening and the ends, remote from the first end section, of the central tubular part and of the outer flow part of the catalyst can be formed by a pipe which passes through a side wall of the connecting section transversely to the longitudinal direction of the exhaust gas aftertreatment device.
Like the outer flow part, the central tubular part of the catalyst can be hollow. As an alternative, the central tubular part may comprise a catalytically active material, like the catalyst part in the form of a jacket, said material being supported in a known manner by a honeycomb body or some other substrate, for example.
In a common housing for the catalyst and the particulate filter, the catalyst part in the form of a jacket, namely the downstream end thereof, can be in direct flow connection with the particulate filter, namely with the upstream end thereof, in the connecting section, thus enabling the catalyst to preheat the particulate filter more directly.
In particular, the catalyst can be an oxidation catalyst or a NOx storage catalyst, and an injector, e.g. an injector for injecting a chemical for selective catalytic reduction (SCR), can furthermore be arranged in the region of the connecting section. Such an injector comprises a certain overall length, and it poses the least interference in the region of the connecting section if it projects outward from the housing wall.
As already mentioned, the exhaust gas aftertreatment device according to the present disclosure is suitable particularly for motor vehicles having an internal combustion engine, wherein the catalyst section is arranged substantially above and the particulate filter section substantially below an exhaust gas outlet opening of the internal combustion engine, and it is suitable particularly for attachment to turbocharged internal combustion engines, wherein said exhaust gas outlet opening is the exhaust gas outlet opening of the exhaust turbocharger, and the connecting section is arranged approximately at the level of the exhaust turbocharger in the engine compartment.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.